Conventional single direction vibratory compactors used for compacting soil, or the like, include a vibrating bottom plate, and a vibration generating unit, consisting of an eccentric shaft carrying an unbalanced weight, is operably connected to the plate. The vibration generating unit generates forces having both vertical and horizontal components which tend to move the plate in a forward direction. Under certain compacting conditions, it may be desirable to move the compactor in both forward and reverse directions, as for example, when the compactor is being used in areas of limited maneuverability.
Many constructions have been proposed in the past to provide reversible drive for compactors. Some systems require the compactor be brought to a full stop in order to reverse directions. Other systems employ a pair of parallel eccentric shafts which rotate in opposite directions with each shaft having an unbalanced weight. By adjusting the angular relation between the eccentric weights on the shafts, the amplitude and/or direction of the vibratory forces can be varied to provide both forward and reverse moment. For example, U.S. Pat. No. 3,262,329 discloses a mechanism for changing the direction of movement of the compactor which is equipped with a pair of eccentric shafts. As disclosed in that patent, a shifting ring is keyed to the eccentric shaft and in its normal position, lugs on the shifting ring will engage lugs on the input gear to thereby provide a driving connection between the gear and the eccentric shaft. By manually moving the shifting ring axially with respect to the eccentric shaft through use of a manual control, driving lugs on the opposite side of the shifting ring will engage an inclined cam which is designed such that after the drive gear has advanced 180.degree. ahead of the eccentric shaft, the lugs will slide off the cam which will enable the lugs on the shifting ring to re-engage the lugs on the drive gear to reinstate the driving connection between the drive gear and the eccentric shaft. With this construction, as shown in the above-mentioned patent, the eccentric shaft thus is lagged 180.degree. behind the other eccentric shaft so that a phase displacement of 180.degree. is obtained which will result in reverse movement of the compactor.